1. Technical Field of the Invention
The present invention relates generally to fuel property detectors, which detect properties of fuel injected by fuel injectors into cylinders of internal combustion engines, and fuel injection systems with such fuel property detectors.
More particularly, the invention relates to a fuel property detector, which detects a property of fuel injected by fuel injectors into cylinders of an internal combustion engine based on a change in the rotational speed of the engine, and a fuel injection system with the fuel property detector.
2. Description of the Related Art
The state of combustion in cylinders of an internal combustion engine depends on the properties of fuel injected by fuel injectors into the cylinders. Moreover, an engine ECU (Electronic Control Device) is generally employed to control combustion in the cylinders of the engine based on the supposition that a reference fuel be used in the engine. Therefore, when the fuel actually injected into the cylinders of the engine has a property (e.g., cetane number) different from that of the reference fuel, the ECU may become unable to suitably control the combustion in the cylinders, causing problems which may include a decrease in the output torque of the engine and an increase in the noise generated by the engine.
For example, when the fuel actually injected into the cylinders of the engine has a lower cetane number than the reference fuel, the output torque of the engine may be decreased. On the other hand, when the fuel actually injected into the cylinders of the engine has a higher cetane number than the reference fuel, the noise generated by the engine may be increased.
To solve the above problem, Japanese Patent First Publication No. 2006-16994 discloses a control apparatus for an internal combustion engine which can detect the cetane number of the fuel actually injected into the cylinders of the engine. More specifically, the control apparatus is configured to: detect an ignition delay of the fuel injected by a fuel injector into a cylinder of the engine by using a cylinder internal pressure sensor; and determine the cetane number of the fuel based on the detected ignition delay.
However, with such a configuration, it is necessary to employ the cylinder internal pressure sensor for detecting the cetane number of the fuel, resulting in an increased manufacturing cost.